Human papillomavirus types 6 and 11 (HPV-6 and HPV-11) are the major aetiological agents of condylomata acuminata. Serological studies of this disease have been difficult to perform and interpret because native, type-specific antigens have not been available. In particular, since these viruses have not been propagated in vitro and sufficient quantities of virions are not present in lesions, virus particles have been difficult to obtain. In the present study, we used HPV-11 particles, obtained from human tumours produced in athymic mice, as antigen in an ELISA to compare antibody responses between 46 patients with biopsyproven condylomata acuminata and 44 controls. The median [interquartile range] of the absorbance values for the condylomata acuminata and the control groups were respectively 0.324 [0.183, 1.029] and 0.118 [0.047, 0.286] (P = 0.0001). Thirty-three per cent of the absorbance values in the condylomata acuminata group were higher than any of those of the control group. Sera from patients whose biopsies contained the papillomavirus common antigen were more reactive than sera from patients whose biopsies did not contain it (P = 0.0014). This study demonstrates the presence of specific antibodies directed at native HPV-11 viral particles in the sera of patients with condylomata acuminata, and describes a test which can be used in future serological studies of this common sexually transmitted disease.